Treatment of a metal-contaminated heavy gas oil with non-adsorbent carbon particles



Ndv. 3, 1959 I R. N. WATTS ETAI. I

TREATMENT OF A METAL-CONTAMINATED HEAVY GAS OIL WITH NON-ABSORBENT CARBON PARTICLES I Filed Nov. 8, 1955 CATALYTIC r25 CRACKING ZONE LIGHT FRACTIONS GAS 2o f 3 221 I4 4 FRACTIONATION T 7 J, ZONE GASOLINE *I! I5 2 I 1; I t I3 CRUDE VACUUM 1* -FRAC. 'STILL I2 I6 5252 ":I C: OUT

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COKING ZVONE J {Ira I16 STEAM Rhea N. Watts 7 Inventors Joseph A. Polack By WJJ- Attorney process.

Patented Nov. 3, 1959 TREATMENT OF A METAL-CONTANIINATED HEAVY GAS OIL WITH NON -ADSORBENT CAR- BON PARTICLES Rhea N. Watts, St. Francisville, and Joseph Albert Polack, Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Application November 8, 1955, Serial No. 545,592

5 Claims. (Cl. 208-88) The present invention relates to a technique for improving the catalytic cracking of heavy gas oil feed stocks normally containing metal contaminants detrimental to the catalytic cracking process. The invention particular ly concerns a process for removing such metal contaminants from catalytic cracking feed stocks'by contact with non-catalytic low surface area granular inert carbon particles, preferably those produced by the fluid coking In a specific and preferred embodiment of the present invention the processes of catalytic cracking, treatment'with the inert carbon, and coking are combined to provide an integrated process.

One of the principal refining operations in commercial use at the present involves the catalytic cracking of so- .called gas oil fractions derived from petroleum. Recently, economic requirements have dictated the necessity of employing higher boiling gas oils as catalytic cracking feed stocks. in-balancedrefinery operations to crack catalytically gas oils containing constituents having an equivalent atmospheric boiling point above about 900-950 F. and up to 1050 F.1300 F. Such heavy, high boiling gas oils have been found to contain nickel, vanadium, iron and other metallic contaminants which, if introduced into a catalytic cracking reactor, serve to seriously degrade the catalyst. Such metal contaminants apparently, occur in heavy gas oils as metal porphyrins which cannot be separated. from gasoil by distillation processes. High-boiling. gas oils of the character identified, whether derived from a crude oil by distillation or derived from other refining operations such as coking, are characterized by inclusion of these metal contaminants. In general, the

heavy gas oils referred to will contain about -20 pounds of metalcontaminants per 1000 barrels, ranging upwardly to as much as 50 pounds per 1000 barrels.

A great deal offeffort is being applied at this time to the development of techniques for removing such metal contaminants from catalytic cracking feed. stocks. The present invention is directed to a novel technique for accomplishing this objective by selectively removing the metal contaminants by means of an'inert granular car-, bonaceous solid. 7

The present: invention is based on exploratory research work in which attempts were made to reduce metallic contaminants .in catalytic cracker feed Without concomitantly. decreasing the volume of gas oil available for cracking purposes. Thus, such processes as prolonged heatsoaking or visbreaking, while reducing ash content, are. not satisfactory for this purpose, for there is significant cracking. at the elevated temperatures needed for these operations, i.e. 900 to 1100 F., and a yield loss audtar formation would be realized. Similarly, treatment of the gas oil with catalystsat elevated temperatures has-been found to reduce substantially the gas oil yield, whileabsorbents are not altogether satisfactory in that -valuable constituents of the oil being treated are removed along with the metal-containingconstituents.

It has now been found that excellent demetallization In particular, it has been found desirable of gas oils may be obtained with concomitant high yield of gas oil product by thermally treating a heavy gas oil at a temperature of 800-850 F. in the presence of inert carbonaceous solids for a relatively rapid throughput rate of 0.5 to 5.0 v./v./hr., or higher under conditions wherein incipient, or mild, cracking occurs. One method of doing this is to heat the oil to these critical temperatures and percolate it through a bed of these solids. The temperature range is critical. Below 800 F., little or no metal removal is obtained. Above 850 F., cracking oc curs to gas and low quality naphtha.

The pressure maintained during the treatment is not critical, and may be in the range of atmospheric to 50 p.s.1.g.

In a specific embodiment of the present invention, use is made of the coke obtained by coking of heavy residual oils.

Use of granular carbon derived from a coking process in this manner is particularly advantageous in permitting an integration of the processes of coking and-catalytic cracking. As a feature of this integrated process, heavy gas oil derived from the coking process, and normally containing metal contaminants, is also treated by the granular carbon treatment of this invention. Such treated coker gas oils, along with treated heavy virgin gas oils, can then be subjected to catalytic cracking.

In order to fully indicate :the nature of this invention, reference will be made to the attached drawing which diagrammatically illustrates a preferred embodiment of the invention constituting a combination process for fractionation of crude oil, coking of residual crude oil fractions, removal of metal contaminants from heavy gas oil fractions of the crude oil and from coker gas oils, and catalytic cracking of the treated gas oils.

As illustrated in the drawing, a crude petroleum oil may be brought into an atmospheric fractionation system 1 through line 2. Fractionation system 1 will be operated to permit removal of light oil fractions overhead through line 3 and of a light gas oil as a side streams product through line 4. The gas oil of line 4 will boil within the range of about 400 to 900 F., and will be substantially devoid of metal contaminants. A residual oil fraction will be removed from fractionation system 1 through bottoms withdrawal 5 constituting the portion of the crude oil boiling above about 900 F.

The residual oil of line 5 is then subjected to vacuum distillation in zone 6; Vacuum still 6 will be operated to permit removal of an overhead product through line 7 constituting a heavy gas oil. This gas oil will be particularly characterized by inclusion of constituents having a normal atmospheric boiling point above about 950 F. and including metal contaminants of the character referred to hereinbefore. The heavy gas oil will have a boiling range Within the temperatures of about 900 to 1300 F. Finally, a heavy residual oil boiling above this range will be removed from vacuum still 6 through line 8.

In accordance with this preferred embodiment of the invention, the residual oil of line 8 is subjected to a coking process. Any desired process may be used for this coking in which the residual oil is heated at temperatures of about 900 to 1100 F., in contact with coke. In this process, residual oil undergoes cracking,

vaporization, and coking. It is particularly preferred to vessel or coker and a heater or burner vessel. In a feed stock is partially vaporized and partially cracked.

Product vapors are removed from the coking vessel and sent to a fractionator for the recovery of gas and light distillates. A gas oil fraction is also segregated for subsequent catalytic cracking. Any heavy bottoms is usually returned to the coking vessel. The coke produced in the process remains in the bed coated on the solid particles. Stripping steam is injected into a stripping zone to remove oil from the coke particles prior to the passage of the coke to the burner.

The heat for carrying out the endothermic coking reaction is generated in the burner vessel, usually but not necessarily separate from the reactor. A stream of coke is thus transferred from the reactor to the burner vessel, such as a transfer line or fluid bed burner, employing 'a standpipe and riser system; air being supplied to the riser for conveying the solids to the burner. Sufiicient coke or added carbonaceous matter is burned in the burning vessel to bring the solids therein up to a temperature suflicient to maintain the system in heat balance. The burner solids are maintained at a higher temperature than the solids in the reactor. About 5% of coke, based on the feed, is conventionally burned for this purpose. This may amount to approximately to 30% of the coke made in the process. The net coke production, which represents the coke make less the coke burned, is withdrawn.

The products of the coking process are withdrawn from zone 9 through line 12 to be subjected to fractionation in zone 13. The fractionation operation will be conducted to permit removal of light gaseous products through line 14 and light liquid products, such as gasoline, through side stream withdrawal 15. A gas oil, particularly constituting a heavy boiling gas oil, will be withdrawn as a side stream product through line 16. This gas oil will contain constituents boiling above about 900 F. and will generally boil within the range of about 400 to 1050 F., or higher, up to about 1300 F. For this purpose, it will be understood that fractionation zone 13 may constitute a vacuum distillation system permitting the segregation of such heavy boiling gas oil without cracking. Finally, heavy residual oil, higher boiling than the gas oil, will be withdrawn as a bottoms product from the fractionation system for recycle to the fluid coking zone through line 17 as described above. Fluid coke may be withdrawn from coking zone 9 through line 1-8 in the quantities required for the treating process ,to be described. Preferably, this coke withdrawal is conducted from the coke burner of the fluid coking operation normally constituting the product fluid coke. This coke is then introduced to treating zone 20 by transfer through line 18. Treating zone 20 will constitute a batch or continuous treating vesselwherein heavy gas oil is contacted with the coke at temperatures in the critical range of 800 to 850 F.

The gas oil to be treated with the coke in zone 20 will particularly constitute the heavy gas oil of line 7 derived from vacuum still 6. In addition, the heavy gas oil of line 16 derived fromthe coking process will be combined with the gas oil of line 7 in line 22. Optionally, some of the light gas oil of line 4 derived from the atmospheric fractionator may also be subjected to treatment in zone 20 by passage through valved line 23. Use of minor portions of this gas oil in zone 29 in amounts of about 5 to 20% may preferably be employed to reduce the viscosity of the heavy gas oil to facilitate contacting and treatment of the heavy gas oil in zone 20. The major portion of the light gas oil of line 4 is passed directly to a catalytic cracking zone through line 24, however.

In one embodiment of the present invention, Zone 20 is a percolation zone and the oil, preheated to the desired temperature, percolates through the bed of the coke granules dispersed in zone 20. This is an important advantage for it avoids a distillation step, and the product may be passed directly to the catalytic cracking stage.

As described then, the heavy gas oil of lines 7 and 16 is brought into zone 20 for treatment with the coke. The treated gas oil is then conducted to the catalytic cracking zone 25 through line 26. Any desired type of catalytic cracking may be carried out in zone 25, although preferably the cracking operation will constitute a fluidized cracking process.

The fluidized solids technique for cracking hydrocarbons comprises a reaction zone and a regeneration zone, employed in conjunction with a fractionation zone.

The reactor and the catalyst regenerator are or may be arranged at approximately an even level. The operation of the reaction zone and the regeneration zone is preferably as follows:

An overflow is provided in the regeneration zone at the desired catalyst level. The catalyst overflows into a withdrawal line which preferably has the form of a U-shaped seal leg connecting the regeneration zone with the reaction zone. The feed stream introduced is usually preheated to a temperature in the range from about 500 to 650 F., by heat exchange with regenerator flue gases which are removed overhead from the regeneration zone, or with cracked products. The heated feed stream is then introduced into the reactor. The seal leg is usually sufficiently below the point of feed oi-l injection to prevent oil vapors from backing into the regenerator in case of normal surges. Since there is no restriction in the overflow line from the regenerator, satisfactory catalyst flow will occur as long as the catalyst level in the reactor is, slightly below the catalyst level in the regenerator when the vessels are maintained at about the same pressure. Spent catalyst from the reactor flows through a second U-shaped seal leg from the bottom of the reactor into the bottom of the regenerator. The rate of catalyst flow is controlled by injecting some of the air into the catalyst transfer line to the regenerator. V

The pressure in the regenerator may be controlled at the desired level by a throttle valve in the overhead line from the regenerator. Thus, the pressure in the regenerator may be controlled at any desired level by a throttle valve which may be operated, if desired, by a differential pressure controller. If the pressure differential between the two vessels is maintained at a minimum, the seal legs will prevent gases from passing from one vessel into the other in the event that the catalyst flow in the 'legs should cease.

The reactor and the regenerator may be designed for high velocity operation involving linear superficial gas velocities of from about 2.5 to 4 feet per second. However, the superficial velocity of the upflowing gases may vary from about 1 to 5 feet per second and higher. Catalyst losses are minimized and substantially prevented in the reactor by the use of multiple stages of cyclone separators. The regeneration zone is also provided with cyclone separators. These cyclone separators usually include 2 to 3 or more stages.

Distributing grids may be employed in the reaction and regeneration zones. Operating temperatures and pressures may vary appreciably depending upon the feed stocksbeing processed and upon the products desired.

Operating temperatures are, for example, in the range from about 800 to 1000 F., preferably about 850"to 950 F. in the reaction zone. Elevated pressures may be employed, but in general, pressures below pounds per square inch gauge are utilized. Pressures generally in the range from 1 to 30 pounds per square inch gauge 200 microns.

. are preferred. Catalystto oil-ratios of about 3 to 10, preferably about 6 to 8. by weight, are used.

The catalytic material used in the fluidized catalyst cracking operation are conventional cracking catalysts. These catalysts are oxides of metals of groups II, III, IV and V of the periodic table.

A preferred catalyst comprises silica-alumina wherein the weight percent of the alumina is in the range from of this invention, the following illustrative example is presented. A heavy gas oil cut, having a rnidboiling point @950" F.,. and containing 2.3 parts per million of nickel and 0.3 parts per million of vanadium, was treated with a variety of catalytic and non-catalytic solids at the critical temperaturerange. 200 cc. fixed-bed unit at 0.6 volume catalyst/volume reactor space per hour (v./v./hr.).

TABLE I Upgrading south La. heavy gas oil [200 cc. unit fixed-bed tests, 0.6 v./v.]

Spent Alumina- Silica Fluid, Catalyst Description Silica Gel Alumina Coke Cracking Catalyst Testing Conditions:

Testing Temperatures, F a 830 830 830 830 D+L 32.5 18; 0 28; 0 11. OTC 37. 6 22. 9 33.. 6 10. Gas Denslt 0.86 0. 74 0.71 0. Wt. Percent Gas 8.0 5. 6 7. 6 3. Wt. Percent Carbon- 7.1 6. 7 7. 1 0. Gas, c.f.[b. 365 297 420 128 Product Yields:

' Gas Oil, Vol. Percent on Feed 62. 4. 77.1 66. 4 89. 4 C to 400, Vol. Percent on Feed- 36. 8 19. 7 30. 7 11. 7 Dry Gas, Wt. Percent on Feed..- 5.19 4. 52 5. 82 2. 73

Hydrogen, Wt. Percent on Feed 0.19 0.17 0. 33 0.02

Inspection of Gas Oil:

. Feed Conradson Carbon 2.25 i 0. 55 0-45 0. 29 1.

Aniline Pt 219. 9 151 167 140 158 Nickel, p.p.m.-- 2. 3 0. 05: 0.05 0.05 0.33

Vanadium p p m- 0. 3 0.05 0. 05 0. 05' 0.05

Iron,p. .m 1.7 L8 7 1.9 1.6 1.8 Sulfur, Percent 0. 41 0. 256 0. 29- v 0. 216. 0. 33

TABLE II 7 Upgrading south La. heavy gas oil Testing Temp., F

Testing Conditions Standard, Except for Temperature Solids Employed Silica Alumina Silica Alumina Fluid Fluid Fluid Gel Gel Coke Coke Coke D+L None None None N one None 11. 0 11. 0 CTO None None N one None N one 10. 6 12. 2 Wt. Percent Gas -None None None None None 3. 2 2. 4 Wt. Percent Carbon None None None None None 0.8 3. 2 Gas c.i'./b None None None None None 128 123 Wt. Percent Gas Oil 100 100 100 100 100 1 .4 86.5 Gas Oil Inspections:

Feed

Nickel, p.p.m 0. 33 0. 2

Vanadium, p.p.m v 0.05

Sulfur. 0.33

Conradson Carbon 1.15 0.75

1 Volume percent.

about 5 to Another preferred catalyst comprises a fluidized bed is maintained Where, in the lower section of the reactor, a dense catalyst phase exists while in the upper area of the reactor a disperse phase exists.

Included in the catalytic cracking system is a product fractionator adapted to segregate gasoline and heavier boiling fractions of the cracked product.

[It will be noted from Table I that the coke reduced the nickel and vanadium content of the feed to substantially the same order of magnitude as was accomplished by the catalysts, such as silica gel, alumina, and silicaalumina spent cracking catalyst. However, it is important to note that the yield of gas oil is substantially higher for the coke than for the catalytic materials. Furthermore, since catalysts require regeneration and the fluid coke is expendable, important economic advantages are,

derived by operating in accordance with the present invention.

To point up clearly the criticality of the temperature, the data in Table II indicate that at a temperature of In order to show the particular advantages and utility 7 5 800 F. or less, littleor no nickel removal is obtained by The tests were carried out in a I cracking purposes.

the solid carbon treatment, and that at temperatures greater than 850 F., yield losses are too high, due to premature cracking to low value thermal naphtha and hydrogen. Thus at 750 F., the coke and also the silica gel, the alumina, and the silica-alumina catalysts failed to decrease the nickel content to less than 1.5 p.p.m.

The aforementioned results show that high yields of low nickel, low vanadium catalytic cracking feed stock may be obtained cheaply with the use of expendable heatcarrying solid carbonaceous particles at incipient cracking conditions from marginal heavy gas oils. In fact, for a given yield of gas oil, the removal of metals, except for iron, is more complete than for any other known process.

Sulfur removal by this process is also significant, and the improvement in Conradson carbon suggests a reduction in nitrogen compounds, aromatics and the like which has contributed to the upgrading of the stock for catalytic The coke provides, in addition, enough surface on which the contaminants such as nickel are deposited, yet not enough surface to adsorb oil products which it is desired to take overhead.

What is claimed is: V

1. The process for the selective removal of metal contaminants present in a heavy gas oil derived from petroleum including constituents boiling above about, 900 F. which comprises contacting said metal-contamh, nated gas oil with an inert granular carbonaceous nonadsorbent solid of low surface area at a temperature of from about 800 to about 850 Ffu'nder conditions to avoid significant cracking of the gas oil and thereafter segregatinga treated gas oil.

2. The process of claim 1 wherein said gas oil is contacted with said carbon granulm in a continuous operation at a throughput rate of 0.5-5.0 v./v./hour.'

3. The process of claim 2 wherein said gas oil is percolated through a bed of said carbon granules.

4. A combination refining process in which a metalcontaminated heavy gas oil including constituents boiling above about 900 F. is treated under non-cracking conditions with inert non-adsorbent carbon particles of low surface area at a temperature in the range of about 800- 850 F., segregating a treated oil, and subjecting said treated oil to catalytic cracking.

5. A combination refining process which comprises fractionating a crude petroleum oil to provide a heavy metal-contaminated gas oil fraction including constituents boiling above about 900 F. and a residual oil fraction, subjecting said residual oil fraction to a coking operation whereby a coked product and a second heavy gas oil 7 boiling above about 900 F. are produced, withdrawing at least a portion of said coke, contacting said first and second heavy gas oils with said withdrawn coke under non-cracking conditions at a temperature in the range of about 800 to 850 F., separating coke from said oil and thereafter subjecting said treated gas oil to a catalytic cracking reaction.

References Cited in the file of this patent UNITED STATES PATENTS 

4. A COMBINATION REFINING PROCESS IN WHICH A METALCONTAMINATED HEAVY GAS OIL INCLUDING CONSTITUENTS BOILING ABOVE 900*F. IS TREATED UNDER NON-CRACKING CONDITIONS WITH INERT NON-ADSORBENT CARBON PARTICLES OF LOW 